Parent for presence node not initialized correctly

[netwrkr95]

Expected Behavior

When a presence node is initialized the pointer to the parent node in the model should be automatically populated

Current Behavior

Traceback (most recent call last):
  File "./nc-create-xe-native-999-ipv6-vrf-def-ydk.py", line 108, in <module>
    crud.create(provider, native)
  File "/usr/local/lib/python2.7/dist-packages/ydk/errors/error_handler.py", line 112, in helper
    return func(self, provider, entity, *args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/ydk/services/crud_service.py", line 30, in create
    return self._crud.create(provider, entity)
  File "/usr/lib/python2.7/contextlib.py", line 35, in __exit__
    self.gen.throw(type, value, traceback)
  File "/usr/local/lib/python2.7/dist-packages/ydk/errors/error_handler.py", line 82, in handle_runtime_error
    _raise(_exc)
  File "/usr/local/lib/python2.7/dist-packages/ydk/errors/error_handler.py", line 56, in _raise
    raise exc
ydk.errors.YPYInvalidArgumentError:  ancestor for entity cannot be nullptr as one of the ancestors is a list. Path: ipv6

Steps to Reproduce

Your Script

def config_native(native):
    """Add config data to native object."""
    definition = native.vrf.Definition()
    definition.name = "test"
    definition.rd = "2:2"
    definition.description = "A YDK App added this IPv6 VRF Definition :-)  "

    # Address-Family Creation
    ipv6 = definition.address_family.Ipv6()
    ipv6.parent = definition.address_family

    export = ipv6.route_target.Export()
    export.asn_ip = "22:22"
    import_ = ipv6.route_target.Import_()
    import_.asn_ip = "22:22"

    ipv6.route_target.export.append(export)
    ipv6.route_target.import_.append(import_)

    definition.address_family.ipv6 = ipv6

    native.vrf.definition.append(definition)

System Information

ydk (0.6.1)
ydk-models-cisco-ios-xe (16.6.1.post1)
ydk-models-cisco-ios-xr (6.2.1)
ydk-models-ietf (0.1.4)
ydk-models-openconfig (0.1.4)

Distributor ID:	Ubuntu
Description:	Ubuntu 16.04.1 LTS
Release:	16.04
Codename:	xenial

[ghost]

Unable to reproduce on ydk 0.7.0

~/>pip list|grep ydk
ydk                     0.7.0    
ydk-models-cisco-ios-xe 16.7.1  
...

[ghost]

Able to reproduce:

def config_native(native):
    """Add config data to native object."""
    definition = native.vrf.Definition()
    definition.name = "test"
    definition.rd = "2:2"
    definition.description = "A YDK App added this IPv6 VRF Definition :-)  "

    # Address-Family Creation
    ipv6 = definition.address_family.Ipv6()

    export = ipv6.route_target.Export()
    export.asn_ip = "22:22"
    import_ = ipv6.route_target.Import()
    import_.asn_ip = "22:22"

    ipv6.route_target.export.append(export)
    ipv6.route_target.import_.append(import_)

    definition.address_family.ipv6 = ipv6

    native.vrf.definition.append(definition)